The 3GPP (3rd Generation Partnership Project) is a project for studying and preparing specifications of mobile communication systems based on networks evolved from W-CDMA (Wideband-Code Division Multiple Access) and GSM (Global System for Mobile Communications). The 3GPP standardized W-CDMA systems as the 3G cellular mobile communication system, and the services have been started sequentially. Further, the 3GPP has standardized HSDPA (High-Speed Downlink Packet Access) with communication rates further increased, and the services have been started. In the 3GPP, using evolution (hereinafter, also referred to as “LTE (Long Term Evolution)” or “EUTRA (Evolved Universal Terrestrial Radio Access)”) of the 3G radio access techniques and wider frequency bands, studies have proceeded on mobile communication systems (hereinafter, also referred to as “LTE-A (Long Term Evolution-Advanced)” or “Advanced-EUTRA”) for actualizing transmission and reception of data of higher rates.
As the communication schemes in LTE, considered are an OFDMA (Orthogonal Frequency Division Multiple Access) scheme for performing user multiplexing using mutually orthogonal subcarriers, and an SC-FDMA (Single Carrier-Frequency Division Multiple Access) scheme. In other words, the OFDMA scheme that is a multicarrier communication scheme is proposed in downlink, and the SC-FDMA scheme that is a single-carrier communication scheme is proposed in uplink.
Meanwhile, as the communication schemes in LTE-A, the OFDMA scheme is considered in downlink, and in uplink, in addition to the SC-FDMA scheme, it is considered to introduce a Clustered-SC-FDMA (Clustered-Single Carrier-Frequency Division Multiple Access, also referred to as DFT-S-OFDM with Spectrum Division Control and DFT-precoded OFDM) scheme. Herein, the SC-FDMA scheme and Clustered-SC-FDMA scheme, which are proposed as the uplink communication scheme in LTE and LTE-A, have characteristics that it is possible to control the PAPR (Peak to Average Power Ratio, transmit power) in transmitting data (information) to within low levels, due to performance (single-carrier performance) of single-carrier communication scheme.
Further, in LTE-A, in contrast to general mobile communication systems in which used frequency bands are contiguous, it is considered to use a plurality of contiguous and/or non-contiguous frequency bands (hereinafter, also referred to as “component carriers (CCs)” or “carrier components (CCs)”) in a complex manner to operate as a single wideband frequency band (also referred to as carrier aggregation). Further, in order for a base station apparatus and a mobile station apparatus to communicate using wideband frequency bands more flexibly, it is also proposed to set different frequency bandwidths on a frequency band used in communications in downlink and a frequency band used in communications in uplink (Asymmetric carrier aggregation) (Non-patent Document 1).
FIG. 9 is a diagram to explain a mobile communication system subjected to carrier aggregation in conventional techniques. Setting the same bandwidth on a frequency band used in communications in downlink (DL) and a frequency band used in communications in uplink (UL) as shown in FIG. 9 is also referred to as Symmetric carrier aggregation. As shown in FIG. 9, the base station apparatus and mobile station apparatus use a plurality of component carriers that are contiguous and/or non-contiguous frequency bands in a complex manner, and are capable of performing communications in a wideband frequency band comprised of a plurality of component carriers.
As an example, FIG. 9 shows that the frequency band (that may be the DL system band (width)) with a bandwidth of 100 MHz used in communications in downlink is comprised of five downlink component carriers (DCC1: Downlink Component Carrier 1, DCC2, DCC3, DCC4, and DCC5) each with a frequency bandwidth of 20 MHz. Further, as an example, FIG. 9 shows that the frequency band (that may be the UL system band (width)) with a bandwidth of 100 MHz used in communications in uplink is comprised of five uplink component carriers (UCC1: Uplink Component Carrier 1, UCC2, UCC3, DCC4, and UCC5) each with a frequency bandwidth of 20 MHz.
In FIG. 9, downlink channels of Physical Downlink Control Channel (hereinafter, PDCCH), Physical Downlink Shared Channel (hereinafter, PDSCH) and the like are allocated to each downlink component carrier.
The base station apparatus allocates (schedules) downlink control information (DCI) to transmit a downlink transport block to be transmitted using the PDSCH to a mobile station apparatus using the PDCCH, and transmits the downlink transport block to the mobile station apparatus using the PDSCH. Herein, in FIG. 9, the base station apparatus is capable of transmitting maximum five downlink transport blocks (that may be PDSCHs) to the mobile station apparatus in the same subframe.
Meanwhile, uplink channels of Physical Uplink Control Channel (hereinafter, PUCCH), Physical Uplink Shared Channel (hereinafter, PUSCH) and the like are allocated to each uplink component carrier.
The mobile station apparatus transmits uplink control information (UCI) including channel state information (CSI) indicative of a channel state in downlink, information indicative of ACK/NACK (Positive Acknowledgement/Negative Acknowledgment) in HARQ in response to the downlink transport block, scheduling request and the like to the base station apparatus using the PUCCH and/or PUSCH. Herein, in FIG. 9, the mobile station apparatus is capable of transmitting maximum five uplink transport blocks (that may be PUSCHs) to the base station apparatus in the same subframe.
Similarly, FIG. 10 is a diagram to explain a mobile communication system subjected to asymmetric carrier aggregation in the conventional techniques. As shown in FIG. 10, different bandwidths are set on a frequency band used in communications in downlink and a frequency band used in communications in uplink, and the base station apparatus and mobile station apparatus use component carriers that are contiguous and/or non-contiguous frequency bands constituting the frequency bands in a complex manner, and are capable of performing communications in wideband frequency bands.
As an example, FIG. 10 shows that the frequency band with a bandwidth of 100 MHz used in communications in downlink is comprised of five downlink component carriers (DCC1, DCC2, DCC3, DCC4, and DCC5) each with a frequency band of 20 MHz, and that the frequency band with a bandwidth of 40 MHz used in communications in uplink is comprised of two uplink component carriers (UCC1 and UCC2) each with a frequency band of 20 MHz.
In FIG. 10, downlink and uplink channels are respectively allocated to downlink and uplink component carriers, and the base station apparatus assigns (schedules) the PDSCH to the mobile station apparatus using the PDCCH, and transmits a downlink transport block to the mobile station apparatus using the PDSCH. Herein, in FIG. 10, the base station apparatus is capable of transmitting maximum five downlink transport blocks (that may be PDSCHs) to the mobile station apparatus in the same subframe.
Meanwhile, the mobile station apparatus transmits the uplink control information including the channel state information, information indicative of ACK/NACK in HARQ in response to the downlink transport block, scheduling request and the like to the base station apparatus using the PUCCH and/or PUSCH. Herein, in FIG. 10, the mobile station apparatus is capable of transmitting maximum two uplink transport blocks (that may be PUSCHs) to the base station apparatus in the same subframe.
Further, in LTE-A, in order for the base station apparatus to measure a channel in uplink, it is studied that the mobile station apparatus transmits a reference signal (hereinafter, also referred to as a Sounding Reference Signal SRS) to the base station apparatus using uplink. Based on the SRS transmitted from the mobile station apparatus, the base station apparatus schedules the mobile station apparatus, and for example, makes determination of allocation of PUSCH resources, modulation scheme and coding rate applied to the PUSCH and the like.
In regard to transmission of SRS by the mobile station apparatus, it is studied that the base station apparatus instructs (requests, triggers) the mobile station apparatus to transmit an aperiodic SRS (hereinafter, also referred to as A-SRS: Aperiodic SRS, Dynamic SRS, or Scheduled SRS) in addition to transmission of periodic SRS (hereinafter, also referred to as P-SRS: Periodic SRS). For example, it is proposed that the base station apparatus instructs the mobile station apparatus to transmit the A-SRS using a downlink control information format for downlink (also referred to as DCI format, downlink grant, or downlink assignment) (Non-patent Document 2). Further, for example, it is proposed that the base station apparatus instructs the mobile station apparatus to transmit the A-SRS using a downlink control information format for uplink (also referred to as DCI format, uplink grant: UL grant or uplink assignment) (Non-patent Document 3).